Photoelectrostatic apparatus



M y 1964 R. M SCHAFFERT 3,132,267

PHOTOELECTROSTATIC APPARATUS Filed Dec. 20, 1961 2 Sheets-Sheet l FIG. 1

e3 6? Q ea 65} 61 69 L 66 M I 1+ 1 Y 164 fin 7o FIG. 6

RESISTANCE (MEGOHMS) 10 2o 50 4o 50 so FIG. 2

INVENTOR ROLAND M. SCHAFFERT FIG. 3 BY A? Aw ATTORNEY y 5, 1964 R. M. SCHAFFERT 3,132,267

PHOTOELECTROSTATIC APPARATUS Filed Dec. 20, 1961 2 Sheets-Sheet 2 United States Patent 3,132,267 PHOTOELECTROSTATIC APPARATUS Roiand M. Schaffert, Saratoga, Califl, assignor to International Business Machines Corporation, New York,

N.Y., a corporation of New York Filed Dec. 20, 1961, Ser. No. 160,864 6 Claims. (Cl. 310--) This invention relates to a photoelectrostaticapparatus, and particularly to a device which utilizes photoenergy to effect a mechanical operation.

In certain types of applications, it is desirable or necessary to obtain a mechanical operation in response to the presence or absence of light. Photocells are a well-known device used for such a purpose. However, previous mechanisms have frequently involved complex arrangements and operation was relatively slow.

It is a principal object of the present invention to provide an improved means which more directly and elficiently utilizes photoenergy to effect a mechanical operation.

It is also an object of the present invention to provide an improved photomechanical device which has high response time.

It is a further object of the present invention to provide a clutch apparatus which is operable directly in response to photoenergy.

It is a still further object of the present invention to provide a motor apparatus device which is operable in response to photoenergy.

The above and other objects are attained in accordance with the practice of this invention by providing first and second mechanical operators which are photoelectrically coupleable. Photoelectric coupling is obtained by making the first mechanical operator electrically conductive While the second member is adapted to adhere to the first operator in response to the application of photoenergy and electric potential.

In one form of the invention the photomechanical device is a clutch. In the clutch embodiment, the first mechanical operator is a driven member such as a band of conductive material. Thesecond mechanical operator is a rotor member having a layer of photoconductive material superimposed on a conductive substrate.

Means is providedfor supporting the rotor member such that the outer surface of the photoconductive layer is in nominal contact with a surface band member. Photoelectric coupling occurs when a potential is applied to the band member and across the photoconductive layer coincidentally with switching of the resistance of the photoconductive layer by application of photoenergy. Preferably the application of potential and photoenergy occurs simultaneously. i

In another form of the invention, the photomechanical device is a motor. As a motor, the first andsecond mechanical operators are preferably rotors. One rotor memher is preferably a conductive memberand the other has a layer of photoconductive material bonded to a conductive substrate. Means is provided for movably mounting the rotors so that the conductive surface of one rotor is in nominal contact with the surface of the photoconduotive layer on the second rotor. A potential is applied to the conductive member and substrate coincidentally with the asymmetrical photoswitching of the photoconductive layer in the region of contact produces a torque whereby the rotor members are turned.

Throughout the description and definition of the invention, the term photoenergy and its variants are used with the intention of including electromagnetic radiantenergy outside the visible portion of the spectrum. The term photoconductive and its variants as applied to materials utilized in the practice of this invention are intended to include materials whose resistance is switchable in response to radiant energy outside the visible energy portion of the spectrum.

Nominal contact here means that the two surfaces, although appearing to be in contact, are nevertheless separated by a thin film of air. It is known that when two surfaces are brought together, they do not make absolute contact except under pressure. The air film between two mechanically smooth surfaces in nominal contact is in the range of 0.5-l micron. Surfaces polished to optical standards and placed in nominal contact are still separated by air gaps of the order of 0.25 micron. When the surfaces are lubricated with lubricants such as oil, the separating film is a liquid.

From the above and the following description, it will be appreciated that a device has been provided for utilizing photoenergy directly to effect mechanical operation. In addition, it will be further appreciated that'a photoelectric clutch and motor have been provided which are inherently simple to construct and operate.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a schematic diagram showing the basic ele ments employed for illustrating the physical principles of the apparatus of the present invention.

FIG. 2 is a graph showing the relationship of photoconductor resistance and force of attraction for a clutch device incorporating the principles of the present invention.

FIG. 3 is a schematic drawing showing a first embodiment of a photoelectrostatic clutch.

FIG. 4 is a partial schematicdiagram showing a second embodiment of a photoelectrostatic clutch.

FIG. 5 is a right side view of the photoelectrostatic clutch of FIG. 4.

FIG. 6 is a schematic diagram for illustrating the principles of a photoelectrostatic motor.

FIG. 7 is a schematic drawing showing a first embodiment of a photoelectrostatic motor.

FIG. 8 is a schematic diagram showing a second embodiment of a photoelectrostatic motor.

FIG. 9 is a further embodiment'showing a photoelectrostatic motor.

FIG. 10 is a schematic drawing of an additional embodiment of a photoelectrostatic motor.

The physical principles underlying the concept of photo electric coupling is explained in connection with FIGS. 1 and 2. In FIG. 1, element 10 comprises a layer of semiconductor material 11 superimposed on a conductive backing forming electrode 12. A second electrode such as metal plate 13 is placed in contact with the surface of the semiconductor material 11. A voltage source 14 is connectable to backing electrode 12 and plate 13 by switch 15- and leads 16 and 17. When voltage is applied between a metal and semiconductor with the surfaces in nominal contact, a normal force of attraction, i.e., a force across the gap, exists. This'force, sometimes called electroadhesion, forms the basis for electrostatic clutch operation. I

' I have determined that the force of electro-adhesion is definable by the following equations:

(1 F=c 14,412,) /2d where The current flowing in the system is definable as 2 i:V /[R e +R where R gap resistance at V =0 a=constant of layer 11 e=2.78 (natural base of logarithm) Using Equations 1 and 2, the effect of changing the resistance of layer 11 on the normal force between layer 11 and plate 13 can be computed. FIG. 2 shows graphically the result of changing resistance of layer 11 on the normal force P where a Voltage of 200 volts has been applied with R =l3 megohms and a=.01. It will be noted from FIG. 2 that there is a very steep drop of the normal force as the resistance of layer 13 is increased, e.g., if the resistance is increased by 2 orders of magnitude, the force F is decreased in the ratio of 7 to 1, an increase of resistance of 3 orders of magnitude will decrease the force by a ratio of about 40 to 1.

In keeping with the above principles and in accordance with the practice of the present invention, a device for utilizing photoenergy to eilect mechanical operation is obtained by having layer 11 formed of a material which is a material which is photoconductive. Materials such as cadmium sulphide, cadmium selenide, and selenium would be suitable as materials for layer 11. A characteristic of such a material which is photoconductive is that in darkness it has a resistivity in the range of -10 ohm-cm, while when exposed to radiant energy such as light its resistivity decreases to a value in the range 10 to 10 ohm-cm.

The first embodiment of a photomechanical device incorporating the above principles takes the form of a photo-operable clutch which, as shown in FIG. 3, comprises a rotor member having a peripheral layer 21 superimposed on a conductive cylinder 22. Rotor shaft 23, which is preferably electrically connected to cylinder 22, is rotatably supported at opposite ends by journal members 24 in a light-sealed housing 25.

A member to be selectively driven by rotor 23 takes the form of a conductive band member 26 which makes operator member 32 of insulating material is attached.

to band member 26 proximate its external end in such a Way that it engages aresilient switch blade 33 which is defiectably operable to engage a second switch blade 34. Electric potential is applied to clutch band 26 and across layer 21 in the following manner:

A voltage source such as a DC battery 35 having one end connected through resistor 36 to ground is connected by lead 37 to conductive band 26. The shaft 23 of rotor 20, since it is connected electrically to cylindrical drum 22, is grounded to complete the circuit. The specific mechanisms for accomplishing the grounding of the shaft 23 and the connection of the battery 35 to band 26 is not shown in order to simplify the description. Suitable mechanisms, however, will readily occur to persons skilled in the art.

For selectively illuminating photoconductive layer 21 of rotor 20, there is provided, in housing '25, a chamber 38 within which is mounted a photoenergy source 39 which, when energized, radiates photoenergy which switches the resistance of layer 21. Suitable bafiling is provided between chamber 38 and the main body portion of housing so that only that portion of layer 21 of rotor 2i) which extends across the opening to chamber 38 is actually exposed to radiant energy. The remaining portion of layer 21, including that portion in nominal contact with band 26,- is maintained in darkness.

The operation of the clutch of FIG. 3 is as follows:

Voltage is applied to band 26 by battery 35, for example, by closing a switch (not shown). At the same time, means for clockwise driving the rotor 2th at a constant speed is set in operation. With energy source 39 deenergized, the entire surface of photoconductive layer 2?. will be in darkness. In the dark, photoconductive layer 21 will have a high resistance. As shown in FIG. 2, the force of attraction between band 26 and rotor 20 is negligible and will not be sumcient to effect coupling. Coupling is obtained with the voltage applied to band 26 when source 3Q is energized and a portion of layer 21 in tle opening of chamber 38 is radiated. The radiation causes the resistance of the layer 21 to drop steeply on the curve of PKG. 2 so that the normal force between band 26 and layer 21 increases sharply. Thus, through photoelectric coupling and due to the clockwise rotation of rotor 21%, the clutch band 26 is moved against the force of spring 3% causing operator 32 to deflect switch blade 33 into engagement with blade 34. It will be noted that in FIG. 3, the energy from source 39 does not radiate a portion of the layer 21 in contact with band 26. However, the. decrease in resistance effected by the radiation in a photoconductive material such as cadmium sulfide persists for a short time in the dark so that the portion of layer 21 having low resistance will contact the surface of band 26 before the high resistance characteristic is restored in darkness. Another feature of the arrangement shown in FIG. 3 is that the resistance of the layer 21 decreases as the intensity of the radiant energy increases. Therefore, the amount of slippage in the clutch can be controlled by regulating the intensity of the radiation.

A second embodiment of the photo-operated clutch is shown in FTGS. 4 and 5. In that embodiment, the clutch comprises first and second disc members 49 and 41. Disc 41 is mounted on a rotatable shaft 42 and disc 41 is mounted on a rotatable shaft 43. The shafts 42 and 43 have a common axis of rotation. Pulley members 44 and 45 may be attached to shafts 4-2 and 43 respectively and provide means for mechanically interconnecting the clutch members to external devices. In the embodiment shown in FIGS. 4- and 5, disc 40 is a conductive circular plate while disc 41 is a composite disc having a photoconductive layer 41a adapted to be maintained in nominal contact with the flat side of plate 40. Superimposed on the back surface of layer 41a is a thin transparent conductive layer 41b. On the back of the conductive layer 41b is a transparent support disc 410. The application of potential is made across layer 41 by connecting battery 46 to disc 40 by lead 47 and to layer 41b by lead 48 which is connected to one side of the battery through resistor 49. As in the. embodiment of FIG. 3, the clutch of FIGS. 4 and 5 is mounted within a housing which maintains the clutch elements in darkness. The radiation of layer 41a of disc 41 is obtained by a photoenergy source such as lamps 5i) mounted on a stationary frame member 51 on the side of disc 41 such that photoenergy penetrates the transparent support plate 410 and conductor 41b While various arrangements for illuminating layer 41 are possible, the preferred arrangement provides plural lamps 50 arranged uniformly around shaft 43 on frame member 51. By such anarrangement, uniformity of illumination is more nearly obtainable so that the normal forces betweendisc 4% and layer 41a are substantially uniform across the gap. Thus, more efficient coupling can be obtained. While the clutch of FIGS. 4 and 5 is not shown enclosed in a housing, it is understood. that such would be provided, if necessary, to shield layer 41a from radiation which would cause photoelectric coupling. An embodiment for incorporating the principles of the present invention in the form of a photoelectrostatic motor may be seen by reference to FIGS. 7-10. The physical:

principles of motor operation are shown in FIG. 6. Referring to FIG. 6, a first motor member 60 having shaft 61 is mounted in suitable manner to be rotatable on a fixed axis. Mounting of member 60 is preferably such that rotation may be bi-directional. As in the case of the clutch devices previously described, motor rotor 60 comprises a conductive cylinder 62 having a layer 63 of photoconductive material superimposed on the outer peripheral surface thereof, and cylinder 62 is electrically connected to shaft 61. A second motor member 64 which is conductive is movably mounted so that it makes nominal contact with the surface 63' along a line parallel to the axis of rotation of rotor 60. Potential is applied across layer 63 by a voltage source such as DC. battery 65 which is connected by leads 66 and switch 67 to shaft 61 and motor member 64. With such an arrangement of rotor 60 and motor member 64 and with switch 67 closed so that a potential is applied across layer 63, motor operation is obtained by asymmetrically illuminating the layer 63.

As shown in FIG. 6, asymmetrical illumination is obtained by a photoenergy projection system which might include photo source 68 and lens 69. The projection system is so arranged that photoenergy is projected onto layer 63 only in that region thereof which is on one side of and immediately adjacent the line of contact between layer 63 and surface of motor member 64. Photoenergy from source 68 and spurious photoenergy from stray sources are prevented by suitable means (not shown) from reaching the layer 63, particularly in the region immediately adjacent to and on the opposite side of said line of contact. By asymmetrical exposure, the normal coupling forces F acting on the rotor 60 in the radiated region are greater than coupling forces F on the non-radh ated region. Thus, an unbalanced torque is produced which rotates rotor 60 and moves motor member 64. In the arrangement shown, rotor 60 moves clockwise and motor member 64 moves from right to left, as shown by arrow 70. Counterclockwise rotation can be obtained by providing a like photoenergy projection on the opposite side of rotor 60. Bi-directional rotation is obtainable by providing two photoenergy projection systems arranged to selectively illuminate opposite sides of rotor 60 asymmetrically. In such an embodiment, a low persistence material such as selenium would preferably be used so that when layer 61, due to rotation of rotor 60, passes from the radiated region to the non-radiated region, a quick diminution in magnitudes of normal forces F to F occurs. However, even with slight persistence, the resistance of layer 61 changes so precipitously, as shown in FIG. 2, that a strong imbalance in forces F and F exists due to exposure from source 65 that a continuous torque is maintainable.

FIG. 7 shows a first embodiment of a photo-operable motor which functions in accordance with the principles illustrated in FIG. 6. In FIG. 7, the motor comprises a pair of rotors 71 and 72 having shafts 73 and 74. Rotors 71 and 72 are mounted in upper and lower positions within a housing 75 by upper and lower journal members 76 and 77 in the usual manner such that the shafts 73 and 74 provide parallel axes of rotation.

The upper motor 71 comprises a conductive cylinder 78 which is electrically connected to shaft 73. A layer 79 of photoconductive material is superimposed on the outer periphery of cylinder 78. Lower rotor 72 is preferably made of conductive material and is electrically connected to shaft 74. A source of potential is applied across layer 79 by a DC. battery 80 having leads 81 and 82 connected toshafts 73 and 74. A switch 83 is provided in circuit of lead 80.

Shafts 71 and 72 are mounted on journals 76 and 77 such that rotors 71 and 72 are in nominal contact along a lineintermediate and parallel to the axes of rotation. Shafts 71 and 72 are insulated from journals 76 and 77 so that potential is not applied to housing 75.

6 In the right side of housing 75, a chamber84 is formed for a photoenergy system. A lamp 85 is mounted on wall 86 of chamber 84. Inside wall 87 of chamber 84 has an' opening in which a lens 88 may be positioned so that With switch 83 closed, motor operation is obtained by energizing lamp 85. Photoenergy from lamp 85 projected onto the region of layer 79 on the right side of the line of nominal contact between rotors 71 and 72 produces a torque causing rotors to rotate in clockwise and coun terclockwise directions respectively. An electrically insulated mechanical external connection to shaft 73 or 74 results in a driving force operable to produce work.

While the embodiment of FIG. 7 is a unidirectional motor, bi-directional operation may be obtained off a single shaft by providing a second chamber on the left side of housing 75 with a second lampsource and means for selectively energizing the lamp sources.

In FIG. 8, the rotor 71 engages a second motor member which takes the form of a conductive belt 90 wound on a pair of spaced apart rotors 91 and 92. Rotor 90 is preferably a conductive cylinder electrically connected to shaft 93. Potential is applied across layer 79 of rotor 71 by a battery 80 connected by lead 82 to shaft 93 and by lead 81 and switch 83 connected to shaft 73 of rotor 71. In the embodiment of FIG. 8, nominal contact is made between layer 79 and belt 90 in the expanse immediate the two rotors. Thus, a nominal contact is made over a surface parallel to axis of rotation of rotor 71.

In FIG. 9, one of the motor members is also a continuous conductive belt 90 wound on a pair of spaced apart rollers. Nominal contact is made with belt 90 along a line over roller 91.

In FIG. 10, a motor member conductive belt 95 is wound around layer 79 of rotor 71 and a roller 96. In the embodiment of FIG. 10, belt 95 is transparent and photoelectric coupling is made by projecting photoenergy from source 85 through lens 88 onto reflecting mirror 97 and through belt 95. A housing 98 which encloses rotor 71 has a chamber 99 within which are mounted lamp 85, lens 88, and mirror 97. Openings 100 and 101 in housing 98 provide passage for belt 95 to roller 96 which may be mounted externally to housing 98. -Roller 96 is preferably a conductive cylinder mounted on a conductive shaft .102. Potential is applied to layer 79 by battery 80 connected thnough leads 81 and 82 with switch 83 to shafts 73 and 102 respectively. By such an arrangement, mechanical connection to motor of FIG. 10 is readily made externally.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is: I I

1. A photo operable motor device comprising in combination a first motor member having a surface comprising a photoconductive layer, a second'motor member having a conductive surface, means for movably supporting said first and second motor members with said photoconductive and said conductive layers in nominal contact, means for producing a motor force whereby said members are moved including means for applying a potential across said layer and means for asymmetrically illuminating said photoconduct-ive layer coincidentally with the application of said potential.

2. A photo-operable motor device comprising in combination a first rotor member, a second rotor member, said first rotor member having a surface comprising a photoconductive layer, said second rotor member having 7 a conductive surface adapted for forming an electrode relative to said layer, means for supporting said rotor members such that said layer and second rotor surface arein nominalcontaot along a line parallel to the axes or rotation of said rotor members, and means for producing aturning torque on said rotors including'means tor asymmetrically photoelectrically coupling said layer and said second rotor member.

3. A photo-operable motor device in accordance with claim 8 in which said means for asymmetrically photoelectrically coupling said rotor members comprises means for projecting a resistance reducing photoenergy onto said layer in the region on one side of said line of nominal contact and means for applying a potential across said layer coincidentally with said illumination from said photoenergy producing means.

4. A photo-operable motor device in accordance with claim 1 in which said first motor member is a rotor member having a peripheral photoconductive layer, and said second motor member includes a movable conductive 20 belt member having a surface in nominal contact with a portion of said layer.

5. A photo-operablemotor device in accordance with claim 4 in which said belt member is supported on spacedapart support rollers and said region of contact with said rotor member is intermediate said support rollers.

6. A photo-operable motor device inaccordance with claim 1 in which said first motor'member is a rotor memlber having a photoconduotive peripheral layer, said second motor member is a transparent belt member having a conductive portion overlaying and in nominal contact with a portion of said layer, and said means for producing a motor force coupling said belt and said rotor member includes means for projecting photoenergy through said belt member onto a region of said layer adjacent one end of said region of nominal contact.

References Cited in the file of this patent UNITED STATES PATENTS 2,916,920 Planer Dec. 15, 1959 FOREIGN PATENTS 437,308 Italy June 30, 1948 34,891 Netherlands Get. 15, 1934 

1. A PHOTO OPERABLE MOTOR DEVICE COMPRISING IN COMBINATION A FIRST MOTOR MEMBER HAVING A SURFACE COMPRISING A PHOTOCONDUCTIVE LAYER, A SECOND MOTOR MEMBER HAVING A CONDUCTIVE SURFACE, MEANS FOR MOVABLY SUPPORTING SAID FIRST AND SECOND MOTOR MEMBERS WITH SAID PHOTOCONDUCTIVE AND SAID CONDUCTIVE LAYERS IN NOMINAL CONTACT, MEANS FOR PRODUCING A MOTOR FORCE WHEREBY SAID MEMBERS ARE MOVED INCLUDING MEANS FOR APPLYING A POTENTIAL ACROSS SAID LAYER AND MEANS FOR ASYMMETRICALLY ILLUMINATING SAID PHOTOCONDUCTIVE LAYER CONCIDENTALLY WITH THE APPLICATION OF SAID POTENTIAL. 